Primary pigmented papillary epithelial tumor of the sella: case report and literature review.

Primary pigmented papillary epithelial tumor of the sella (PPPET) is a recently identified tumor entity that commonly originates in the sella. To date, only three cases have been documented. These tumors are characterized by a papillary structure and significant melanin granule deposition. Notably, molecular characterization of PPPET remains unreported in the literature. A 42-year-old male presented with left-sided visual impairment for 2 weeks. Neuroimaging revealed a round sellar hyperdense mass. Histologically, the tumor exhibited minimal nuclear atypia and was characterized by a papillary architecture and obvious intracellular hyperpigmentation. Immunophenotypically, tumor cells showed diffuse positivity for S-100 and Melan-A, partial or focal positivity for synaptophysin and CD56, and negativity for TTF-1, GFAP, EMA, cytokeratins, and pituitary hormones. The Ki-67 proliferation index was low. The whole exome sequencing (WES) analysis revealed multiple potentially pathogenic gene mutations (AGAP3, DDX10, BBX, NFATC4, SLC6A6) in tumor tissues. Large genomic rearrangements (LGRs) involving PRKRA (exon6-8 del) and SKA3 (exon2-8 del) were detected. Genomic instability analysis indicated whole genome doubling (WGD) and aneuploidy in the tumor cells. Copy number variation (CNV) analysis demonstrated extensive copy number abnormalities at the chromosome arm level in tumor tissues. No classical mutations associated with known tumor types of the sella and choroid plexus were detected. PPPET has unique morphologic, immunohistochemical, and molecular genetic characteristics. Our findings suggest that PPPET may be an independent neurooncological entity.